


skin deep aquarium

by sharkfish



Series: suckerfish [1]
Category: Supernatural
Genre: Alpha Castiel (Supernatural), Alternate Universe - Modern with Magic, Castiel Has Tentacles, Cecaelias, Consentacles, I don't know how to tag tentacle-related sex acts, Love Confessions, M/M, Mating Cycles/In Heat, Non-Traditional Alpha/Beta/Omega Dynamics, Octopus Castiel (Supernatural), Octos Are Known, Sappy, Tentacles, octo cas
Language: English
Status: Completed
Published: 2018-01-23
Updated: 2018-01-23
Packaged: 2019-03-08 10:33:07
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,804
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13456398
Author URL: https://archiveofourown.org/users/sharkfish/pseuds/sharkfish
Summary: Cas moves closer, the end of a tentacle wrapping around Dean’s ankle as his hands tilt Dean’s chin up. “There are things I’m not supposed to tell you.”“I know,” Dean says.“The biology of our genders is different, as is our social behavior surrounding it.”“I know, Cas.”Cas tugs at Dean’s ankle and kisses him like it was hurting him not to. “I’m an alpha,” Cas says.





	skin deep aquarium

**Author's Note:**

> when you get into tentacle stuff it can be a mixed bag and i dunno how to tag this, but there isn't any belly bulging or multiple-tents-in-one-orifice happening this fic. nothing weird. ;) 
> 
> thanks to [robotsnchicks](http://robotsnchicks.tumblr.com) and [miraakcultist](http://miraakcultist.tumblr.com) for the beta, and [unforth](http://unforth-ninawaters.tumblr.com) for awakening this in me.
> 
> this fic has sorta existed in my head for a long time, but [this art by saawek](http://reallyelegantsharkfish.tumblr.com/post/169854799680/saawek-the-kinky-mess-dean-has-a-mate-with) definitely inspired some aspects of it.

Dean’s still not entirely sure what Cas does during the time they’re not together. Even now, Cas is intensely private. Dean’s not surprised by that — humans know so little about cecaelia life and culture — but he thought the boyfriend thing might override that. So far, it hasn’t.

Every now and then Cas tells Dean he won’t be around for a few days, but he never offers an explanation and just shakes his head tersely when Dean tries to ask.

It’s been longer than usual this time. On days four and five, Dean sits down at the dock and watches the sun set, hoping for Cas, but the only movement is a couple coots further out in the cove. Dean spends half of day six pissed as hell, but it slips into resignation as he pulls the Impala into his driveway. 

Whatever he thought he had with Cas is done. The finality of the thought has him sucking in a breath and dropping his forehead against the steering wheel. (The last time they saw each other, Dean was in the middle of talking about some movie or another when he looked up at Cas and suddenly thought,  _ Holy shit. I’m in love with Cas _ . So much for that.)

Dean’s feet are heavy as he drags himself into the house, but then he slips and nearly cracks his head open in the entryway, and when he steadies himself on the wall, Cas is in front of him. 

“Goddammit, Cas,” Dean says automatically. “I’m going to kill myself one of these days if you keep —” 

“Dean,” Cas says. 

Dean had been so surprised to see him that he hadn’t noticed what’s happening to Cas’s tentacles. Dean’s used to them changing — his favorite is the way they go  _ glittery _ when Dean touches him, even if it’s just a kiss on the cheek — but he’s never seen them like this, flowing in color from burgundy red to black to witch purple, the luminescence catching the light in random places like scattered freckles. “Are you — are you ok?” Dean says, reaching out for him. 

“You’re upset,” Cas says. 

Dean ducks his head down. “Yeah, well. I thought you were breaking up with me via the silent treatment.” 

Cas moves closer, the end of a tentacle wrapping around Dean’s ankle as his hands tilt Dean’s chin up. “There are things I’m not supposed to tell you.” 

“I know,” Dean says. 

“The biology of our genders is different, as is our social behavior surrounding it.”

“I know, Cas.” 

Cas tugs at Dean’s ankle and kisses him like it was hurting him not to. “I’m an alpha,” Cas says. 

When Dean meets Cas’s eyes, they’re the same deep red as his tentacles. Dean startles backwards, nearly slipping again. “What the fuck, Cas?!” 

“I’m in rut,” Cas says. “I need my mate.” 

“Your  _ what _ ?” 

Cas pulls him in for another almost violent kiss. One of Cas’s tentacles slides up Dean’s shirt, pausing to suck a line of red splotches across his hip before brushing across a nipple. “Let me be explicit,” Cas says. “I need to fuck you.” 

“I need you to slow down a minute. What’s going on?” 

Cas scowls in frustration but pulls out from under Dean’s shirt. “It’s part of our mating cycle. In theory, a mated pair’s heat and rut align to maximize fertility.” 

“Ok,” Dean says. 

“It’s — difficult — to be separated from a mate during rut.” 

“What do you mean, ‘mate’?” 

Cas tilts his head to the side. For a moment his eyes pale towards blue again, and he suddenly looks unsure. “Aren’t we? Aren’t we mates?” 

“I don’t know what that means. That sounds — it sounds serious.” 

Suddenly Cas isn’t touching Dean at all. “It is. Cecaelia mate for life.” He looks away, mouth drawn tight. “I thought you knew that.”

“No, wait,” Dean says. “Hang on. I mean, I’m — I’m human. I know you have to resent me for that.”

“I chose you,” Cas says. “I chose you before you even saw me the first time.” 

“Cas,” Dean says. “What do you need?”

“I need to fuck you again and again until you can’t take any more.” 

Dean’s eyes widen and he licks his lips. “Ok. In bed though. You’re not messing up my knees again on the floor.”

“Good. I like your bed,” Cas says, turning to glide down the hall in that alien-grace way of his. 

Dean kicks off his boots and then follows helplessly after Cas, just like he’s been doing since they first met. Cas’s tentacles are still rapidly changing color and Dean stares at them all the way into the bedroom, itching to touch. 

“Take off your clothes,” Cas says. 

Dean strips obediently with Cas’s blood-red eyes on him. “How do you want me?” 

“Hands and knees,” Cas says. 

Dean takes a last long look at Cas — the end of his tentacles are doing this little twitching thing they do when he wants to wrap them around Dean — and climbs into bed. Cas follows him, a tentacle sliding around each of Dean’s thighs to pull his legs wider apart. He knows Cas likes the human parts of him most when they’re like this, uncovered, and Cas proves it again by spreading Dean’s cheeks and leaning in to lick over Dean’s hole.

Cas spends a long time slicking up Dean with his mouth, until Dean is riding back against him as much as he can with tentacles still holding his legs apart. More are touching him, too, the tip of one brushing over the curve of Dean’s ear, one stroking through his hair, one slipping around his hip to leave more suction marks across his stomach. Cas is, as always, completely overwhelming even before they’ve really started. 

A tentacle prods at Dean’s mouth and he opens obediently. Cas groans against where he’s still working his tongue in and around Dean’s hole as Cas pushes into his mouth. He tastes distinctly non-human, but it’s good, and the way Cas makes Dean feel and the way Cas tastes-feels-smells-sounds are all wrapped together in Dean’s brain anyway, chemical responses ricocheting off each other.  

Cas kisses Dean’s lower back as one of his tentacles caresses Dean’s balls and then moves backwards until it’s brushing past his hole. Dean shudders and takes the tentacle in his mouth deeper.

Sometimes Cas teases Dean forever, but now he gives Dean what he wants right away. One of the suction cups on the underside of Cas’s tentacle presses over Dean’s hole, and — _ fuck fuck fuck _ , Dean chants in his head since his mouth is too busy to say it. 

_ Nothing  _ has ever felt like this. Dean jerks and would collapse if it weren’t for most of Cas’s tentacles wrapped all around Dean’s body, easily supporting his weight. They’re sucking, too, and in the morning Dean will be covered in perfect round bruises, evenly-spaced tattoos marking him Cas’s. 

A tentacle wraps delicately around Dean’s cock and Dean groans around the one in his mouth. Cas strokes him slowly, running his hands up Dean’s trembling back. “Can I fuck you now?” Cas says.

When the tentacle pulls out of his mouth, Dean says, “Please.” 

Cas’s extra limbs are extremely convenient at moments like this, when he can use a tentacle to reach in the drawer for lube without taking his hands off of Dean. He runs his fingers into Dean’s hair and pushes Dean’s head down to bite at the back of his neck. 

Cas slicks up his fingers first and slips one into Dean immediately. They’re always a little desperate for each other, but Dean can tell Cas is feral with need in a way he’s never been before. 

“I’m ok, you can just fuck me,” Dean says. 

“I can’t hurt you,” Cas says. “I won’t.” 

Dean shivers as a second finger presses inside him. The tip of a tentacle slides across Dean’s lower lip and he opens his mouth for it. One curls around Dean’s neck, too, not applying any pressure, but Cas likes Dean vulnerable for him. Vulnerable for his  _ mate. _

Dean pulls the tentacle out of his mouth and says, “No marks on my neck.” 

Cas stills in a way that tells Dean he had forgotten all about the conversation they had months ago. (“Cas, there’s literally no way for me to explain this to anyone. There’s no curling iron lie for this.” And then he had to explain what a curling iron is.) “I won’t,” Cas says, and the sucking around the column of Dean’s throat stops. 

Dean is mostly held immobile by Cas, but he manages to stick his tongue out far enough to lick the tip of the tentacle still near his mouth, trying to tease Cas into fucking his mouth again. Cas rumbles into Dean’s ear and pulls out his fingers. They’re replaced immediately with the teasing touch of Cas’s cock, and as it starts to work into Dean, slow and steady, Cas says, “I’m claiming you tonight.” 

Dean shudders and Cas presses one of his palms flat on Dean’s lower back, urging him to arch further. The tentacle pulls out of Dean’s mouth so he can breathe easier and it drags spit down Dean’s chin as it goes. 

“Can I have you?” Cas says. 

Dean manages to rasp, “Yeah, anything.” 

Cas makes that rumbling sound again and thrusts a little harder, a little deeper, until Dean’s head falls heavy between his shoulders. He can see the otherworldly shimmer lighting up Cas’s tentacles. The color is still flowing from red wine to indigo. They change all the time — like a mood ring, Dean thinks, though he can’t always identify exactly what each different color means — but he’s never seen them turn red as rich as now. 

Cas covers Dean’s back with his own weight, shifts the tentacle around Dean’s neck downwards so he can bite down hard just under Dean’s jaw. “I’m sorry,” Cas says while he soothes the bite with soft kisses. “This is going to be fast. I should’ve been here sooner.” 

“It’s good,” Dean says. “I don’t care, it’s so good.” 

Cas chokes on a moan and turns his head to breathe harshly into Dean’s hair. “Can I come in you?” 

“Yeah, c’mon,” Dean says, and he cries out when Cas fucks him harder, just a little deeper. 

Dean and Cas are still finding all the ways they can make each other feel good, and the newest thing they’ve discovered is the way Dean whimpers and whines and thrashes in Cas’s grasp when Cas presses a sucker on the bottom of the head of Dean’s cock, the same spot Cas just barely grazes with his teeth when he goes down on him. Cas is holding Dean’s head up by the tentacle around his throat so Dean can’t see, but he knows what it looks like anyway, pre-come dripping over the tip of the tentacle on his cock. 

“I love the way you taste,” Cas says. 

There’s not ever a time that Dean forgets Cas isn’t human. Even when he’d just seen Cas’s head and shoulders above the water, before he knew what Cas’s tentacles feel like all around and in him, he knew he and Cas were from separate worlds. Every now and then, though, Cas says something to remind Dean of how different they really are. This is one of those moments, because Cas is talking about the liquid he’s coaxing out of Dean’s dick. Cas is talking about the taste buds on the velvet skin of his tentacles. 

Cas tightens around Dean’s neck — and his chest, and his thighs, and his cock — and the suckers all over him seize up when Cas comes. He groans Dean’s name and wraps his hand around the base of Dean’s cock, stroking what he can while still suckling on the head. Dean feels slick and sloppy where Cas is still fucking into him, and he comes fast. Dean goes limp, trusting Cas to hold him afloat. 

The tentacle around Dean’s neck loosens and then slips away. The one on his dick lets up just before pleasure could turn into pain, but it’s only withdrawing to rub through Dean’s come. It’s another cecaelia behavior that used to be so foreign but doesn’t seem strange at all anymore. Dean had always assumed it was some sort of possessive thing, maybe a mixing of their scents, but he didn’t realize until today the implications of walking around smelling like Cas, of Cas swimming around smelling like him. 

Cas lays Dean down carefully and then tucks up behind him, draping his tentacles all around Dean, each of them tracing aimless patterns on Dean’s skin. It’s Cas’s fingers that nudge between Dean’s legs to rub where Dean is leaking Cas’s come. Cas pushes two fingers back into him and strokes slowly, carefully. 

“Let me keep you full of my come all the time,” Cas says. 

Dean laughs and relaxes further into him. “Baby, some of us have bills to pay.” 

Dean touches one of Cas’s tentacles, tugging it up to his face to nuzzle and kiss. Cas is the color of coal again, hardly glowing, and Dean slides his hand up the tentacle to where it’s too thick for him to wrap his fingers around. 

A sucker latches on to Dean’s cheek. It’s a quick touch, but Dean turns his head to the side and elbows backwards anyway. “What the fuck!” Dean says. Cas is chuckling at his back. “I fucking hate that!” 

“Sorry,” Cas says, but he sounds more smug than contrite. 

“I wish you were ticklish,” Dean says. “Then I could get you back.” 

“Human bodies are so strange and weak,” Cas says. 

“Don’t insult me when I’m trying to do a post-coital bliss thing.” Dean says, craning his neck to show Cas his smile. Sometimes he’s still not sure if Cas can tell when he’s kidding. 

Cas smiles back and kisses the corner of his mouth, curls his tentacles around him tighter. “I won’t tease you anymore until the bliss is over.”

 

Once Dean’s brain is back online, he gets up for a beer. Cas asks for one, too, even though Dean always ends up finishing his. Cas’s eyes are their normal shade again. Cerulean, Dean thinks it’s called. 

Dean sits up against the headboard and Cas abandons his bottle immediately to lay his head on Dean’s thigh. Dean strokes his fingers absently through Cas’s hair and Cas rumbles happily. By now Dean is used to the way Cas touches Dean everywhere at once all the time. He used to think it was a cecaelia thing, but now he’s wondering if it’s a cecaelia-with-their-mate thing. When did Cas decide he wanted to be Dean’s?

“Can we talk about — uh, whatever is going on? With you?” Dean says. 

Cas sighs. “If we must."

“You said it’s — I don’t go into rut, so how…?” Dean’s not even sure what he’s trying to ask. 

“No, you would be an omega,” Cas says. 

“A  _ what? _ ”

“You would go into heat, not rut.”

“Ok, whatever. But we can’t make babies. I mean — can  _ you?  _ Can you get pregnant?” 

A sucker grabs at Dean’s cheek again and he shoves it away. Cas is definitely fucking with him.  “No, Dean, I can’t get pregnant.”

“If neither of us can get pregnant, what’s this talk about fertility or whatever?”

“Do you really think you don’t have mating instincts that affect you regardless of the actual viability of reproduction? Not only with me, but you’ve mentioned men you’ve been with,” Cas says. “Sex exists for procreation, but your species and mine do it even when that’s not possible.”

“Ok, that’s fair. So you’re just like extra horny and, uh, really good at making babies.”

“Don’t be crude.”

“Look at me.”

Cas is slow about it, but he sits up to meet Dean’s eyes. Dean can’t stand to put that look on his face, like he’s ready for rejection. (It’s the same face he made after the first time he kissed Dean, sitting next to each other at the end of the dock, legs and tentacles dangling in the water.)

“Hey,” Dean says. “This is ok. I’m not freaked out. We’re — mates, right? That’s what you said.”

“Yes,” Cas says quietly. 

“I can help you with this. You said that, too.” Cas nods, still looks apprehensive. “So let me help you. Is this why you leave sometimes?”

“Yes.”

“Why didn’t you tell me?”

“I’m not supposed to, but mostly I just didn’t want you to know.”

“Why not?”

Cas looks away. “I didn’t want you to know another way we’re different.”

“Baby, I’m covered in tentacles all the time. I can’t exactly forget.”

Cas half-smiles. “We don’t touch like this except for with our mates.”

“I wondered about that.” 

Cas’s eyes are starting to darken again and he watches Dean’s mouth as he runs the tip of a tentacle across it, then he pulls it away from Dean’s lips to kiss him, deep and slow. 

“You wanting to fuck me again?” Dean says.

“Yes.”

“Gotta be a little gentler with me this time.”

Cas backs away, his eyes wide. “Did I hurt you?”

“Not really. I mean, I liked it. I always like when you fuck me. But if we’re going to be doing this all weekend, maybe take it a little easy.”

“Ok,” Cas says. “Lay down.”

Dean sets his beer aside — doesn’t even complain that he didn’t get to finish — and rearranges on the bed to Cas’s satisfaction. Cas spends a long time just tracing his fingertips over the marks he’s left all over Dean’s body, then bends to kiss the ones laid diagonally across Dean’s stomach, wrapping around his hip. 

“You’re so beautiful,” Cas says. 

Dean knows people think he’s attractive, generally. He’s never had trouble finding hookups. But Cas says it in a worshipful way no one else ever has, and he presses kisses all over Dean like he wants to do it forever, like he’s not starting to glitter and change in the way Dean now knows means  _ alpha needing his mate.  _

“You too,” Dean says, reaching to touch Cas’s hair. (Dean asked him once how it could be so goddamn soft in a lake with no hair products. Cas shrugged like the topic didn’t interest him.)

Cas nuzzles up to Dean’s mouth and kisses him, the rest of him starting to touch with intent again, tentacles brushing over the tops of Dean’s thighs until Dean’s legs part, then sucking on the soft skin between them. 

“I’m probably not getting hard again already,” Dean says. “But that doesn’t mean I’m not likin’ this.”

“That’s ok,” Cas says, burrowing his face in Dean’s neck. 

“Cas,” Dean says. “Why are you hiding?”

Cas prods gently at Dean’s hole where he’s still leaking a little come and lube, and when he lifts his head up, his eyes are burning. 

“Your eyes, that’s like that thing that happens to your tentacles when we kiss and stuff, right?” 

“Yes.” 

“Cool,” Dean says, and pulls him down for a kiss. 

Cas’s cock pulls away and when it touches Dean again, it’s slicked up to slide inside him. Cas shudders when he breaches Dean, and Dean smiles up at him. “Feels good?”

Cas rolls his eyes. It’s even more melodramatic with them red, and Dean really loves him. 

Before Cas can say anything sarcastic back, Dean covers Cas’s mouth with his own again. Cas is gentle as promised, slow about pushing deeper. Dean runs his hand up and down Cas’s tentacles, mostly because he loves the way Cas tightens all around him when Dean offers him pleasure.

“Feels really good for me,” Dean whispers, and then gasps as a sucker latches on to his balls. 

Cas’s face is still almost close enough to kiss, but he reaches a tentacle to Dean’s mouth again. Dean gives the underside a long, flat lick. “ _ Dean, _ ” Cas says. 

Dean circles his tongue from one sucker to another, watching Cas’s expression, watching Cas watch him. The thrusts into Dean get a little less steady and Cas makes that weird purring noise deep in his throat as Dean goes back to sucking the end of the tentacle. Cas replaces it with his mouth again, and his tentacle wraps around Dean’s neck, stroking the line of his jaw softly. 

Cas moves between Dean’s legs so he can get closer, pressing tight down their whole bodies, tentacles wrapped all around Dean, cradling him. Cas is fucking into him harder while they kiss, a little past the  _ gently _ Dean asked for, but it’s so fucking good. 

“You  _ are _ hard again,” Cas says against Dean’s mouth. 

“Fuck, Cas. You know I’m crazy for you.” 

The tentacle around Dean’s neck keeps tightening a tiny bit, then releasing again, like it’s taking a lot of restraint to keep from leaving bruises all over his throat. “You make me feel things I don’t understand,” Cas says. 

Dean wraps his arms around Cas’s shoulders, kisses him again and again. “Touch me, please. Please.” 

Cas wraps a tentacle around Dean’s cock, squeezing and sucking. Dean really didn’t think there was any way he was going to get hard again, much less come, but he’s panting and moaning for it the same way he did for the first guy to ever fuck him, cramped in the back of the Impala. 

“You’re going to come again,” Cas says, but for once he sounds more awed than smug. 

“Harder, just a little,” Dean says, and then, “Holy Christ, just like that.” 

Dean comes first, so hard he’s almost too dazed to feel Cas coming hot and deep, groaning into Dean’s neck. They pant together, still all wrapped up in each other, Dean running his fingers through Cas’s hair. 

Cas is still making that rumbling noise when he stretches out next to Dean, pulling him close with his tentacles until they are nose to nose. 

“Do cecaelias usually kiss each other?” Dean says.

Cas tilts his head and squints at Dean. “Sometimes.” 

“Not like you and I do?” 

“No, I don’t think so.” 

“Do you hate it?” 

“Why would I hate it?” Cas asks, frowning.

“If it’s not something you usually do. We don’t have to.” 

“But I like it. Don’t you like it too?” 

Dean smiles and gives Cas a short, sweet kiss, then another, tongues sliding against each other. Cas is smiling, a blinding light with bright blue eyes, when Dean pulls away. 

Dean says softly, “Do you know what humans say to their mates?” 

Cas probably knows more about humans than Dean does, and they both know it, but he smiles indulgently all the same. “No, what do humans say to their mates?”

“I love you.” 

Out of the corner of Dean’s eye, he sees Cas’s tentacles change rapidly to deep purple and shimmering. 

**Author's Note:**

> [reallyelegantsharkfish on tumblr](http://reallyelegantsharkfish.tumblr.com/)
> 
>  
> 
> [transformative works policy](http://reallyelegantsharkfish.tumblr.com/post/167716491355/transformative-works-policy)
> 
>  
> 
> Even before we met  
> when the assignment was to partner up in ice water,  
> and keep our heads above it  
> I’d watch boys with girls  
> take the shallow end of the 8th grade like  
> suckerfish  
> swapping skin deep aquarium air tubes  
> trying to make each others shivers fit.  
> We don’t swim that way.  
> Never gonna.  
> Flockprinter,  
> You have been a long time comin’
> 
> from [“flockprinter” by buddy wakefield](https://www.youtube.com/watch?v=Ey52siBzSBo)
> 
> buddy, i'm sorry for involving you in this.


End file.
